编写一个求定积分的通用函数，用它分别求以下几个积分：

Question

double integral(double a, double b, double (*f)(double));

Answer 1

#include<stdio.h>
#include<math.h>
double f1(float x)
{
return (1.0*x + x*x);
}
double f2(float x)
{
return (2.0*x*x + 3.0*x);
}
double f3(float x)
{
return(exp(x) + 1);
}

double integral(double a, double b, double(*f)(double))
{
double c, s;
c = (a + b) / 2;
s = (b - a) / 6 * (f(a) + 4 * f(c) +f(b));
return s;
}

int main()
{
double a, b;
printf("请输入积分下限a的值：");
scanf("%lf", &a);
printf("请输入积分上限b的值：");
scanf("%lf", &b);
printf("%lf\n", integral(a, b, f1));
printf("%lf\n", integral(a, b, f2));
printf("%lf\n", integral(a, b, f3));
}

Answer 2

不知道怎么输入积分号，书面可以写给你看